A diamond-like carbon film (hereinafter, called “amorphous carbon film”) is a film excellent in abrasion resistance and slidability and having high strength. For this reason, the amorphous carbon films are used in various fields, including protective films of various devices such as cutting tools and dies. Also, it has been known that a second layer is provided on an amorphous carbon film to make it possible to improve the heat resistance, oxidation resistance, abrasion resistance, lubricity and the like. For these characteristics, amorphous carbon films are expected to be used in a wide variety of fields.
However, there is a problem in that the adhesion between an amorphous carbon film and a second layer is insufficient. As a method of improving the adhesion between the amorphous carbon film and the second layer, there has been known a method of using, for a second layer to be provided on an amorphous carbon film, a material condensation-reacting with hydroxyl groups on the surface of the amorphous carbon film, such as a silane coupling agent. Silanol groups generated by hydrolysis of a silane coupling agent are formed into a polymer by self-condensation and are condensation-reactable with hydroxyl groups on the surface of an amorphous carbon film.
Amorphous carbon films need to be provided with uniform water repellent power or oil repellent power, on their surfaces.
When water repellency is imparted to an amorphous carbon film, there have been known techniques of modifying the surface of the amorphous carbon film with fluorine, for example, by a method of using a gas containing fluorine as a raw material gas during film formation, or a method of subjecting an amorphous carbon film to a surface treatment using a gas containing fluorine after film formation of the amorphous carbon film. However, depending on the degree of addition amount of fluorine, the hardness of the film greatly decreases. In addition, it is unfavorable to use fluorine-based gases which adversely affect film formation devices and human bodies/environments. To solve this problem, methods of introducing fluorine into a surface of an amorphous carbon film without using a fluorine-based gas have been studied. For example, Patent Literature 1 discloses that a surface treatment agent containing an ultra-stable perfluoroalkyl radical is used as an active component in surfaces of amorphous carbon films prepared on surfaces of a variety of solid materials, without using fluorine gases, thereby introducing fluorine into the surfaces of the amorphous carbon films.
Further, to improve the adhesion between an amorphous carbon film and a second layer to be provided on the amorphous carbon film, there have also been proposed methods of improving adhesive force of an amorphous carbon film itself. For example, Patent Literature 2 describes that a first layer comprising an amorphous carbon film containing Si excellently adheres to a second layer comprising a polyamideimide layer containing MoS2. In addition, Patent Literature 3 discloses that it is possible to obtain a biomolecular fixation material having stable fixability by using an amorphous carbonaceous film containing Si, without recourse to a chemical modification treatment.